Sulfur group sensitized emulsions



United States Patent C 3,320,069 SULFUR GROUP SENSITIZED EMULSIONS Bernard 1). Illingsworth, Rochester, N.Y., assiguor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 18, 1966, 821'. No. 535,350 16 Claims. (Cl. 96-407) This application is a continuation-in-part of application Ser. No. 788,769, filed January 26, 1959 now abandoned, and of application Ser. No. 364,308, filed May 1, 1964 and now abandoned.

This invention relates to the preparation of photographic emulsions which are distinguished by the presence of a water-soluble thiocyanate compound (excluding, of course, thiocyanate compounds that contain cations that are known to be deleterious to photographic emulsions) present as a silver halide grain ripener, either during the actual precipitation of the light-sensitive silver halide or by its addition immediately after the precipitation, but in all instances the Water-soluble thiocyanate compound used is present with the silver halide before the secondary photographic emulsion producing steps of washing and digestion. The digestion of our emulsion is done in the presence of a sulfur group sensitizer and preferably with also a gold or other noble metal salt as an auxiliary sensitizer therefor.

It is known that the silver halide crystals of conventional photographic emulsions are sensitive to light, both on the surface and internally. In certain types of photographic processes it is desirable that the surface of the silver halide crystals have a sensitivity considerably greater than that of the internal portions thereof.

One object of my invention is to provide a process for preparing gelatin-silver halide emulsions the silver halide crystals of which are of low internal sensitivity. Another object of my invention is to provide a process for preparing gelatin-silver halide emulsions in which a watersoluble thiocyanate is employed in their preparation and they are sensitized with sulfur and gold sensitizers. A further object of my invention is to provide a silver bromoiodide photographic emulsion containing between 1 and 10 mole percent iodide which when coated on a support at a silver coverage between 300 and 1000 mg. per square foot and then exposed on an intensity scale seusitometer and processed for 5 minutes in Kodak Developer DK-SO has a log speed greater than 250 and a remainder resulting from subtracting the granularity value from the log speed greater than 180. Other objects of my invention will appear herein.

I have found that photographic emulsions composed of silver bromoiodide and gelatin in which the silver bromoiodide contains bet-ween l and mole percent of iodide which emulsions when coated on a support at a silver coverage between 300 and 1000 mg. per square foot and then exposed on an intensity scale sensitometer and processed for 5 minutes in Kodak Developer DK-SO have a log speed greater than 250 and a remainder resulting from subtracting the granularity value from the log speed greater than 180 are obtained by the following combination of conditions in their preparation:

(1) Silver nitrate and alkali halide are run simultaneously into a gelatin solution containing a water-soluble thiocyanate in which solution the halide is kept in excess throughout the precipitation. The precipitation is normally accomplished in the presence of a slight excess of halide, the preferred range being 4-20 mole percent of water-soluble excess halide per mole of silver present.

(2) The emulsion is of the bromoiodide type, the total iodide being preferably 1-10 mole percent per mole of silver halide in the emulsion.

(3) The silver halide is digested with a sensitizer 01 the sulfur group such as with a labile sulfur, selenium or tellurium sensitizer, or preferably with both a sulfur, selenium or tellurium sensitizer and a gold or other noble metal salt, at an elevated temperature.

The preparation of photographic emulsions in accordance with my invention involves: (1) preparing the silver halide dispersion, (2) ripening the silver halide grains during their formation or immediately thereafter by subjecting to an elevated temperature, (3) washing the soluble salts from the silver halide grains prepared thereby, (4) sensitizing with a sensitizer of the sulfur group such as with a sulfur, selenium or tellurium sensitizer and with a gold or other noble metal salt as an auxiliary sensitizer therefor.

The silver halide dispersion in accordance with my invention is conveniently prepared under non-ammoniacal conditions by running a aqueous solution of a watersoluble halide and an aqueous solution of silver nitrate simultaneously into a solution of gelatin or a gelatin derivative which solution may contain a water-soluble thiocyanate such as potassium thiocyanate or ammonium thiocyanate or the thiocyanate may be present in the alkali halide solution. In the precipitating operation the water-soluble halide is kept in excess of that necessary for combining with the silver which is present throughout the precipitation operation. Silver bromoiodide is thus formed, the amount of iodide provided being such that the iodide is 1.0l0 mole percent of the total silver halide formed, the remainder of the halide used being a water-soluble bromide such as potassium bromide or sodium bromide.

The dispersion can be prepared either in gelatin or in an aqueous solution of gelatin derivative as described in Yutzy and Frame Patent No. 2,614,928.

The silver halide dispersion is then washed to remove water-soluble salts therefrom. This washing may be carried out by the method described in the Yutzy and Frame patent referred to or if gelatin was employed as the peptizing material in prepared the silver halide dispersion, washing may be carried out by the methods described in US. Patents Nos. 2,614,929, 2,618,556 or 2,489,341 or by setting the composition by chilling, noodling and washing the noodles in cold water.

After the silver halide grains have been washed, they are suspended in distilled water or in a solution of gelatin and distilled water and the emulsion is sensitized by the addition of a sulfur group sensitizer such as a sulfur, selenium or tellurium compound or a sulfur, selenium or tellurium sensitizer and a gold or other noble metal salt and heating at an elevated temperature such as F., for a time, such as 10-20 minutes.

The water-soluble thiocyanate may be supplied in the preparation of the silver halide dispersion as described above. If desired, however, it may be added to the silver halide at any time prior to its washing. In chemically sensitizing the washed photographic emulsion, any sensitizer of the sulfur group may be used, e.g. the sulfur sensitizers described in Sheppard US. Patent 1,574,944, issued March 2, 1926; Sheppard et al. US. Patent 1,623,499, issued April 5, 1927; or the Sheppard and Brigham US. Patent 2,410,689, issued November 5, 1956. Some sulfur group sensitizers useful in digesting emulsions prepared in accordance with my invention are: allyl thiourea, thiourea, isopropyl, thiocarbamate, thioacetamide, sodium thiosulfate, allyl isothiocyanate, phenyl isothiocyanate, allyl selenourea, dimethyl selenourea, colloidal selenium, colloidal tellurium, allyl tellurourea and phenyl thiourea. The noble metal sensitizer which is added may be auric trichloride, potassium aurithiocyanate, potassium chloroaurate, gold sulfide, ammoni- [11 chloropalladate, potassium chloroplatinite, or any E the noble metal sensitizers that are recognized in the rior art as having this property, e.g. the gold sensitizers escribed in the Waller et al. US. Patent 2,399,083, isied April 23, 1946 or the Damschroder US. Patent ,642,361, issued June 16, 1953.

The amount of water-soluble thiocyanate employed my be any value from -50 grams per mole of silver alide, the optimum being about 20 grams per mole of .lver halide. If the thiocyanate is employed in the prepaation of the silver halide dispersion, it may be added rholly or in part to the solution of halide which is run no the water solution of peptizing agent. However, if esired, all or most of the thiocyanate can be introduced no the water solution of peptizer into which the silver .itrate and halide solutions are run. As is common in he preparation of silver halide dispersions the dispersing lquid is agitated while the silver nitrate and water-soluble talide is being run therein. The thiocyanate may, if lesired, be supplied to the silver halide after the disperion has been formed but in any case must be supplied hereto before it is washed.

To form the emulsion the silver halide grains are distersed in a vehicle of a protein material such as gelatin ind is sensitized by digesting with a sulfur group sensitizer )r a sulfur group sensitizer and a noble metal sensitizer. It is to be understood that the various operations de- .cribed are carried out under darkened conditions to avoid Yogging the photosensitive silver halide.

The emulsions in accordance with my invention have remainder, resulting from subtracting granularity value From log speed, greater than 180. It is preferred in these :mulsions that the log speed be between 280 and 400 and that the remainder resulting from subtracting granuarity value from log speed be within the range of 180 and 220. The log speed equals 100 (1log E) when E .s the exposure measured in meter-candle seconds necesiary to produce a density equal to 0.3 above fog. Granularity H equals K determined by the method described by L. A. Jones et al. in Journal of the Optical Society of America, volume 47, No. 4, pages 312-321, April 1957.

Kodak Developer DK-50 (page 2558 of the Handbook of Chemistry and Physics, 30th Edition) is composed of the following components:

Water at about 125 F. ounces 64 Nunethyl-p-aminophenol sulfate grains 145 Desiccated sodium sulfite ounces 4 Hydroquinone grains 145 Sodium metaborate-4H O (1 oz.) do 145 Potassium bromide do 30 Water to make 1 gallon.

The photographic emulsions prepared in accordance with my invention have various advantages over conventional types of photographic emulsions. For instance, in color films and color reversal films, emulsions in ac cordance with my invention are adapted for reversal development as well as for use in reversal development processes in black and white photography. The grain size of uniformity of emulsions prepared in accordance with my invention is excellent, fewer fine grains being present than in the usual types of photographic emulsions. The grains of these emulsions have a more uniform lattice structure than those of the usual types of emulsions as may be determined by their X-ray diffraction pattern. As a corollary these emulsions are less susceptible to pressure desensitization. Emulsions prepared in accordance with my invention have shown themselves to have a high forced development speed and a speed to graininess advantage over emulsions previously described in the art.

The following examples illustrate the preparation of emulsions in accordance with my invention.

4 Example 1 Solution A:

Phthaloylated gelatin grams 48 KBr .do 12 KI do 20.4 Sodium thiocyanate do 10 Dissolved in 5000 cc. of distilled water at 50 C.

at 30 C. Solution B:

KBr grams 238 Distilled water to total volume of 1300 cc. Solution C:

Silver nitrate .grams 340 Distilled water to total volume of 1310 cc.

at 30 C.

Solution A was vigorously stirred and maintained at a constant temperature of 50 S. Solutions B and C were run in uniformly over a period of 40 minutes, the introduction of B having been started 10 seconds before the introduction of C and finished not more than 30 seconds before the finish of the C run.

A silver halide dispersion was obtained. The silver halide dispersion obtained was cooled to 33 C. and was coagulated by lowering the pH and washing in the manner described in US. Patent 2,614,928 of Yutzy and Frame. The washed coagulum was redispersed in 2000 cc. of distilled water at 40 C., whereupon a solution of 470 grams of gelatin in 2500 cc. of water at 40 C. was added and then a solution of 1.54 grams of Thymol in cc. of 50% methyl alcohol-water. The total weight of the mass was adjusted to 6.36 kg. by adding distilled water.

The pH was then adjusted to 6.4 and there was added thereto a sulfur sensitizer (allyl thiourea) and a gold sensitizer (auric trichloride). The emulsion was then heated for 12 minutes at 60 C. After cooling to 40 C. a small amount of saponin as a coating aid was added to the emulsion which was coated onto a cellulose acetate support at the rate of coverage of 200 sq. ft. per mole of silver halide.

Distilled water to total volume of 2055 cc. at

30 C. Solution C:

Silver nitrate 340 Distilled water to total volume of 2100 cc. at 30 C.

Solution A was vigorously stirred at a constant temperature of C. and solutions B and C were introduced therein over a period of 120 minutes, starting B 10 seconds before C and finishing the B run less than 1 minute before the C run.

The silver halide dispersion obtained was cooled to 33 C. and the silver halide was washed by the coagulation technique of US. Patent 2,614,928 of Yutzy and Frame. The washed coagulum was redispersed in 1500 cc .of distilled water at 40 C. A solution of 501 grams of gelatin in 2000 cc. of distilled water at 40 C. was added followed by a solution of 2.31 grams of Thymol in cc. of 50% methyl alcohol-water. Distilled water was added to bring the weight of 6.12 kg. and the pH was adjusted to 6.4 The emulsion was sulfur and gold sensitized as described in Example 1. The emulsion was digested by heating at 55 C. for 25 minutes and was cooled to 40 C. Saponin was added to the emulsion to aid in coating and the mass was coated onto a cellulose acetate -film support at a coverage of 200 sq. ft. per mole of silver halide.

was maintained at 75 C. while solutions 13 and C were introduced therein over a period of 40 minutes starting B seconds before C and finishing the B run less than 1 minute before the C run.

jected to pressure such as by means of rollers. For instance, /z of a strip from each of the above examples was subjected to pressure by passing the half between 2 weighted rollers. The entire strip was then given a negative exposure in an Eastman Ib sensitometer and was processed for 5 minutes in Kodak DK-SO Developer.

The following results indicate the lack of any appreciable desensitization by the use of pressure which compares favorably with conventional silver halide photographic emulsions.

Unpressured Pressured Relative Gamma Fog Relative Gamma Speed (E) Speed (E) Example 1 100 1. 65 11 85 1. 66 Example 2- 501 2. 29 14 417 1. 94 Example 3 380 99 10 355 1. 03

Example 4 Four emulsions were prepared in the same manner except that the amount of thiocyanate and the temperature were varied. The conditions used Were as follows:

Emulsion Emulsion Emulsion Emulsion 5312 5313 5314 5315 Solution A:

Grams phthaloylated gelatin 25 25 Milliliters, H1O 2, 000 2, 000 2, 000 2, 000

Grams, KBr 1 1 12 12 Grams, KI 4. 1 4. 1 4. 1 4. 1

Grams, KCNS 2O 10 1O 10 Temperature, 0-- 80 8O 68 58 Solution B:

Milliliters, H2O"--- 695 695 695 695 Grams, KBr 114. 5 114. 5 114. 5 114. 5

Grams, KI 6. 1 6. l 6. 1 6. 1 Solution C:

Grams, AgNOa 170 170 170 170 Milliliters, H9O 698 698 698 698 The silver halide dispersion which formed was cooled to 33 C. and washed by coagulation with a lowered pH and removed of the water-soluble salts in accordance with the procedure described in US. Patent 2,614,928. The coagulum from which the water-soluble salts had been removed was dispersed in 2000 cc. of distilled Water at C. and there was added a solution of 420 grams of gelatin in 2500 cc. of distilled water at 40 C. and 1.54 grams Thymol in 70 cc. of methyl alcohol-water. Distilled Water was added to bring the Weight to 6.36 kg. and the pH was adjusted to 6.4. The emulsion was sensitized by the addition of sulfur sensitizer and gold sensitizer in accordance with the procedure described in British Patent 636,140. The emulsion was digested by heating at C. for 22 minutes, cooled to 40 C., coating aid was added thereto and it was coated onto a cellulose acetate film support at a coverage of 200 sq. ft. per mole of silver halide.

The emulsions prepared in accordance with my invention are free of any appreciable desensitization when sub- Solution A Was vigorously stirred and the temperature was maintained at that designated while solutions were introduced therein over a period of 40 minutes, starting B 10 seconds before C and finishing the B run less than 1 minute before the C run. The emulsions were washed and chemically sensitized as described in Example 3. A sample of each of these emulsions was then coated on a cellulose acetate support at a coverage of 700 mg. of gelatin and 480 mg. of silver per square foot. A sample of each coating was exposed on an intensity scale sensitometer, processed for 5 minutes in Kodak Developer DK-SO, fixed, washed, and dried. The log speed and granularity of each coating was determined as described supra. The results are found in the table following Example 5.

Example 5 This is an example of emulsions of the type previously described in the prior art. Four emulsions were prepared as described in Example 3 except that all of the alkali halide salts were included in Solution A and the thiocyanate salt was omitted from each preparation.

Solution A was vigorously stirred and the designated emperature was maintained while Solution C was introluced therein over the periods designated in the various :mulsions.

The silver halide dispersions thus obtained herein. The log speeds and granularity value of each :oating and the remainder obtained by subtracting granu- :arity value from log speed were determined with the following results:

obtained with no appreciable increase in fog; and Part 4 was selenium and gold sensitized by adding 0.6 mg. of dimethyl selenourea and 2.5 mg. of colloidal gold sulfide per mole of silver halide and heating the emulsion at 65 C. until optimum sensitivity had been obtained with no appreciable increase in fog.

Each part was panchromatically sensitized by the addition of cyanine dyes. Samples of each of Parts 1-4 were coated on cellulose acetate film support at a laydown of 540 mg. of silver and 1235 mg. of gelatin per square foot.

A sample of each of the coatings was exposed on an intensity scale sensitometer, processed for 5 minutes in Kodak Developer DK-SO, fixed, washed, and dried. The log speed and Emu]. Emul. Emul. Emul. Emul. Emul. Emul. Emul. 5308 5309 5310 5311 5312 5313 5314 5315 Log speed 337 315 304 283 336 320 314 296 Granularity 163 139 129 111 151 129 119 109 Log speed minus granularity 174 176 175 172 185 191 195 187 Example 6 9O granularity of each coating was determined as described able increase in fog; and Part 3 was selenium and gold sensitized by adding .40 mg. of dimethyl selenourea and 1.5 mg. of colloidal gold sulfide per mole of silver halide and heating the emulsion at 65 C. until optimum sensitivity had been obtained with no appreciable increase in fog. Each part was panchromatically sensitized by the Samples of each of Parts 13 addition of cyanine dyes.

were coated on cellulose acetate film support at a laydown of 540 mg. of silver and 1235 mg. of gelatin per square foot. A sample of each of the coatings was exposed on an intensity scale sensitometer, processed for 5 minutes in Kodak Developer DK-50, fixed, washed, and dried. The log speed and granularity of each coating was determined as described above with the following results:

Type of Chemical Log Speed sensitizing Log Speed Granularity Minus Granularity None 196 140 56 Sulfur-gold 328 140 188 Selenium-gold 344 140 204 60 Example 7 A silver halide photographic emulsion was prepared as described in Example 4 in accordance with Emulsion No. 5315 of that example in which the emulsion was washed but not chemically sensitized and divided into four parts: Part 1 was not chemically sensitized; Part 2 was sulfur sensitized by adding 5.3 mg. of sodium thiosulfate and then heating the emulsion at 65 C. until optimum sensitivity had been obtained with no appreciable increase in fog; Part 3 was sulfur and gold sensitized by adding 5.3 mg. of sodium thiosulfate and 2.04 mg. of potassium chloroaurate per mole of silver and then heating the emulsion at 65 C. until optimum sensitivity had been above with the following results:

The invention has been described in considerable de tail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A silver bromoiodide-gelatin photographic emulsion in which the iodide comprises 1-10 mole percent of the halide, said emulsion being sensitized with a sulfur, selenium or tellurium sensitizer, said emulsion when coated on a support at a silver coverage of between 300 and 1000 mg. per square foot and exposed on an intensity scale sensitometer and processed for five minutes in Kodak Developer DK-SO at 68 F. has a log speed of 280-400 and a remainder resulting from subtracting its granularity value from its log speed of between and 220.

2. The emulsion of claim 1 in which the iodide comprises approximately 6.2 mole percent of the halide.

3. The emulsion of claim 1 which is sensitized with a sulfur sensitizer.

4. The emulsion of claim 2 which is sensitized with a sulfur sensitizer.

5. The emulsion of claim 1 which is sensitized with a selenium sensitizer.

6. The emulsion of claim 2 which is sensitized with a selenium sensitizer.

7. The emulsion of claim 1 which is also sensitized with an auxiliary noble metal sensitizer.

8. The emulsion of claim 1 which is sensitized with a sulfur sensitizer and an auxiliary noble metal sensitizer.

9. The emulsion of claim 1 which is sensitized with a selenium sensitizer and an auxiliary noble metal sensitizer.

10. The emulsion of claim 1 which is prepared in the presence of a water-soluble thiocyanate compound as a silver halide grain ripener.

11. A method of preparing washed silver bromoiodide photographic emulsions, the silver halide grains of which have a high ratio of surface to internal sensitivity, which comprises:

(a) simultaneously introducing a solution of silver nitrate and a solution of an alkali metal halide into a nonammoniacal solution of protein peptizer, the halide which is 99-90 mole percent of bromide and 110 mole percent of iodide neing kept in 420 mole percent excess therein per mole of silver present;

('0) contacting the silver halide grains thus formed with 5-50 grams per mole of silver of a water-soluble thiocyanate which does not have a deleterious eflfect on the emulsion;

(c) subsequently washing the soluble salts from the silver halide grains;

(d) digesting the grains by subjecting a dispersion thereof to an elevated temperature; and

(e) sensitizing the silver halide suspension with a sulfur, selenium or tellurium sensitizer.

12. The method of claim 11 in which the sensitizer is either allyl thiourea, thiourea, isopropyl thiocarbamate, thioacetamide, sodium thiosulfate, allyl isothiocyanate, phenyl isothiocyanate, allyl selenourea, dimethyl selenourea, colloidal selenium, colloidal tellurium, allyl tei lurourea or phenyl thiourea.

13. The method of claim 11 wherein an auxiliary nobl metal sensitizer is employed in the sensitization step.

14. The method of claim 13 in which the noble meta sensitizer is either auric trichloride, potassium aurithio cyanate, potassium chloroaurate or gold sulfide.

15. The method of claim 13 wherein a sulfur sensitize and a gold sensitizer are employed in the sensitizatiol step.

16. The method of claim 15 in which the sulfur sensi tizer is either allyl thiourea, thiourea, isopropyl thiocar bamate, thioacetamide, sodium thiosulfate, allyl isothio cyanate, phenyl isothiocyanate or phenyl thiourea.

References Cited by the Examiner UNITED STATES PATENTS 1,574,944 10/1926 Sheppard 96-10i 2,743,183 4/1956 Lowe et a1. 96-10% 3,260,605 7/1966 Sutherns 96l0E NORMAN G. TORCHIN, Primary Examiner.

J. H. RAUBITSCHEK, Assistant Examiner. 

1. A SILVER BROMOIODIDE-GELATIN PHOTOGRAPHIC EMULSION IN WHICH THE IODIDE COMPRISES 1-10 MOLE PERCENT OF THE HALIDE, SAID EMULSION BEING SENSITIZED WITH A SULFUR, SELENIUM OR TELLURIUM SENSITIZER, SAID EMULSION WHEN COATED ON A SUPPORT AT A SILVER COVERAGE OF BETWEEN 300 AND 1000 MG. PER SQUARE FOOT AND EXPOSED ON AN INTENSITY SCALE SENSITOMETER AND PROCESS FOR FIVE MINUTES IN KODAK DEVELOPER DK-50 AT 68*F. HAS A LOG SPEED OF 280-400 AND A REMAINDER RESULTING FROM SUBSTRACTING ITS GRANULARITY VALUE FROM ITS LOG SPEED OF BETWEEN 180 AND
 220. 11. A METHOD OF PREPARING WASHED SILVER BROMOIODIDE PHOTOGRAPHIC EMULSIONS, THE SILVER HALIIDE GRAINS OF WHICH HAVE A HIGH RATIO OF SURFACE TO INTERNAL SENSITIVITY, WHICH COMPRISES: (A) SIMULTANEOUSLY INTRODUCING A SOLUTION OF SILVER NITRATE AND A SOLUTION OF AN ALKALI METAL HALIDE INTO A NONAMMONIACAL SOLUTION OF PROTEIN PEPTIZER, THE HALIDE WHICH IS 99-90 MOLE PERCENT OF BROMIDE AND 1-10 MOLE PRESENT OF IODIDE BEING KEPT IN 4-20 MOLE PERCENT EXCESS THEREIN PER MOLE OF SILVER PRESENT; (B) CONTACTING THE SILVER HALIDE GRAINS THUS FORMED WITH 5-50 GRAMS PER MOLE OF SILVER OF A WATER-SOLUBLE THIOCYANATE WHICH DOES NOT HAVE A DELETERIOUS EFFECT ON THE EMULSION; (C) SUBSEQUENTLY WASHING THE SOLUBLE SALTS FROM THE SILVER HALIDE GRAINS; (D) DIGESTING THE GRAINS BY SUBJECTING A DISPERSION THEREOF TO AN ELEVATED TEMPERATURE; AND (E) SENSITIZING THE SILVER HALIDE SUSPENSION WITH A SULFUR, SELENIUM OR TELLURIUM SENSITIZER. 